The invention relates to a method for producing a metal melt in a metallurgical vessel, in particular an iron or steel melt, feed substances, which contain metals and/or metal oxides, being charged in solid and, if appropriate, molten form into the metallurgical vessel, the main part of the energy necessary for the melting and, if appropriate, finish-reduction of the feed substances being applied electrically and/or by the combustion and/or gasification of carbon-containing materials. The invention relates, further, to a multi-functional lance for use in a method according to the invention.
EP 0 257 450 A2 teaches a method for increased energy introduction and current saving in arc furnaces for steelmaking. In this case, free oxygen jets emanating from blow-on devices are used for the post-combustion of the furnace waste gases and under-bath nozzles are used for moving the bath. Coal for the formation of CO is blown in via a hollow electrode or under-bath nozzles and the oxygen for the formation of CO is likewise supplied to the melt through under-bath nozzles.
A disadvantage, here, is the high outlay in terms of apparatus for blowing in the coal, the formation of CO and post-combustion. Furthermore, the under-bath nozzles required, which are loaded with oxygen, are exposed to high wear and, correspondingly, have only a short service life.
There have also been many attempts to make devices and methods available for heating and blowing for metallurgical purposes and for combustion in metallurgical reactors.
Thus GB 1,015,581 discloses a burner with a central oxygen duct, with a fuel supply duct surrounding the latter and with an outer annular duct for oxygen. The fuel and oxygen are intermixed immediately after emerging from the respective mouths. According to GB 1,015,581, the burner is provided for use in all top-blowing oxygen steelmaking methods.
However, such a burner is unsuitable for sucking in furnace gases to an appreciable extent for post-combustion, so that it can contribute nothing or only little to improving the energy balance.
AT 402,963 B describes the combustion of fuel by means of a specially designed burner. As a result of the rapid intensive swirling of the fuel together with oxygen in a chamber of the burner, the outflowing mixture very soon becomes relatively slow over the running distance of the mixture jet. Such a burner therefore has relatively short flame length and in this case, once again, neglects to suck in furnace gases, so that this, too, can contribute little to improving the energy balance. Furthermore, such a burner is suitable only to a limited extent for the refining of a steel melt.
WO 91/00366 describes a method and a device for heating a metallurgical furnace, an inner oxygen duct being encased annularly by a fuel duct. In this case, the fuel is supplied by means of an inert to weakly reducing carrier gas. Here too, no possibility is given for the post-combustion of furnace waste gases by sucking them into the burner jet or for the refining of the melt.
The object of the present invention is, therefore, to provide a method and a device for use in such a method which avoid the disadvantages known from the prior art. In particular, a method is to be provided, which requires less energy, both electric and fossil, than known methods in order to produce a metal melt and which can be carried out in a shorter time, and multi-functional lances are to be provided, by means of which the method according to the invention can be carried out and which, furthermore, are kept compact and simple in terms of construction and, when a repair is necessary, can be repaired again easily and simply.
This object is achieved, according to the invention, by means of the combination of the following features:
that
A) in a combustion step, additional energy is supplied to the feed substances by the blowing-in, taking place by means of one or more multi-functional lances, and combustion of gaseous and/or liquid carbon-containing materials and oxygen-containing gas,
B) in a cutting and melting step, the solid feed substances are cut and partially melted by the intensified blowing-in, taking place by means of the multi-functional lance or lances, of oxygen-containing gas,
C) in a refining step, the melted feed substances are refined by the intensified blowing-in, taking place by means of the multi-functional lance or lances, of oxygen-containing gas,
D) in a carbon blow-in step, alloying carbon and/or additional energy is supplied to the feed substances by the blowing-in, taking place by means of the multi-functional lance or lances, and, if appropriate, combustion of fine-grained and/or dust-like solid carbon-containing materials,
E) in a post-combustion step, the waste gases from the metallurgical vessel are afterburnt by the blowing-in, taking place by means of the multi-functional lance or lances and directed away from the respective multi-functional lance in at least two of the three spatial directions, of oxygen-containing gas into the waste-gas space of the metallurgical vessel,
F) in a solid blow-in step, the necessary substances are supplied to the feed substances by the blowing-in, taking place by means of the multi-functional lance or lances, of fine-grained and/or dust-like solid aggregates and/or alloying agents, in order to achieve the desired composition of the metal melt,
steps A) to F) being carried out, depending on the composition of the feed substances and on the desired composition of the metal melt, selectively in any desired combination, in particular in succession and/or in reverse order and/or simultaneously and/or omitting individual steps of steps A) to F).
By means of the method according to the invention, metal melts can, according to an advantageous feature, be produced, for example, in electric furnaces or converters or melt-down gasifiers or in a particularly energy-saving and time-saving way. Furthermore, ladles or vessels for the conversion of slag may be used as metallurgical vessels. The respective metallurgical vessel may be under overpressure, atmospheric pressure, underpressure or a vacuum.
The multi-functional lances used for the method according to the invention make it possible to carry out the individual method steps flexibly, with free choice and, in particular, also simultaneously.
There is an increase in the use of solid metal carriers for producing melts, in particular steel melts, since these materials are already metallic and therefore no longer have to be reduced at a high outlay. Such solid metal carriers are therefore recirculated to an increasing extent. In particular, such materials, such as scrap, pig iron, cast iron, etc., are processed in electric furnaces, so that it is particularly important to improve the operation of electric furnaces. Rapid melting-down and refining in order to set short furnace cycle times are important for achieving low heat losses and electrode consumptions and for the uninterrupted feeding of modern continuous casting plants. Moreover, the melting capacity of electric furnaces is also to be increased as a result of the controlled parallel introduction of electric and fossil energy.
These requirements are satisfied by the method according to the invention.
According to an advantageous feature of the method according to the invention, one or more multi-functional lances are used jointly with burners and/or refining lances and/or post-combustion lances and/or, in the case of electric furnaces, under-bath nozzles and/or hollow electrodes and/or, in the case of converters, side nozzles, which in each case are known per se.
It is thereby possible that burners and/or refining lances and/or post-combustion lances cover, as it were, the basic loads of a corresponding method step and, in addition, energy is introduced, melting carried out, refining carried out, coal and/or alloying agent blown in, waste gas afterburnt, etc., at particularly important points by means of the multi-functional lance or lances additionally used, for the purpose of achieving a rapid method flow.
In a further advantageous embodiment of the method according to the invention, in a solid blow-in step, one or more of the following substances is or are blown into or onto the partially or completely melted feed substances: metal ores, such as chrome ore, nickel ore and manganese ore, metal oxides, such as nickel oxide, vanadium oxide and chrome oxide, iron carbide, calcium carbide, aluminium, FeSi, FeCr, FeMn, oil-containing scale, slags, slag formers, dusts from dedusting systems, grinding dusts, metal chips, deoxidants, shredderlight fraction, lime, coal, coke and sponge iron, in each case in fine-grained and/or dust-like form.
If a plurality of substances are to be blown in, these may be blown, intermixed or separately, into/onto the partially or completely melted feed substances. The introduction of a mixture of substances may, for example, then be somewhat advantageous when metal ores and/or metal oxides are blown in jointly with deoxidants.
Preferably, in a post-combustion step, the blowing-in of oxygen-containing gas takes place in a periodically fluctuating and/or pulsating manner.
As a result, the post-combustion of the waste gases from the metallurgical vessel can be carried out particularly efficiently, so that the energy released at the same time is transmitted with high efficiency to the feed substances and is not lost to the waste-gas system which is even relieved of thermal load.
According to a further embodiment of the method according to the invention, in a carbon blow-in step and/or a solid blow-in step in an electric furnace, the jet from a multi-functional lance is directed into the vicinity of the point of impingement or into the point of impingement of solid material, which is charged onto the melt via an orifice in the furnace roof, or of an arc on the melt.
According to an equally advantageous embodiment, in a carbon blow-in step and/or a solid blow-in step in a converter, the jet from a multi-functional lance is directed into the vicinity of the point of impingement or into the point of impingement of an oxygen jet from a further lance or a side nozzle on the melt.
The two last-mentioned embodiments are advantageous particularly when large quantities of ores, NiO, oxidic fines and dusts, which in each case may also be mixed with coal, have to be reduced. The reduction and melting of the feed substances are particularly accelerated by the introduction of carbon at the point or points where the greatest supply of energy also simultaneously takes place.
According to a particularly advantageous feature of the method according to the invention, one or more of the method steps A, B, D, E and F are carried out by means of a multi-functional lance essentially simultaneously with a refining step, particular preference being given to carrying out a combustion step essentially simultaneously with a refining step. By xe2x80x9cessentially simultaneouslyxe2x80x9d is meant, here, an at least partial time overlap of the two method steps.
In addition to the intensified blowing-in of oxygen-containing gas, as a result of which the melted feed substances are refined, liquid and/or gaseous carbon-containing substances and oxygen-containing gas are also blown in and the carbon-containing substances are burnt.
According to a further advantageous feature of the method according to the invention, in a refining step during the production of preferably alloyed iron melts with a low carbon content, steam and/or an inert gas, such as nitrogen, and/or rare gases are blown into or onto the partially or already completely melted feed substances, in addition to the intensified blowing-in of oxygen-containing gas.
Consequently, the CO partial pressure and therefore iron slagging, as well as the slagging of alloying elements, in particular, chrome slagging, are reduced appreciably.
According to one embodiment of the method according to the invention, in a carbon blow-in step for the production of iron melts or steel melts with a low carbon content, the carbon-containing materials are blown at low velocity only onto and into the slag located above the melt.
Additional refining of the melt is thereby avoided here. The carbon-containing materials then serve primarily for the foaming of the slag.
As a result of a further advantageous embodiment of the method according to the invention, a liquid blow-in step (G) is carried out during one or more of the method steps A, B, C, and E, burnable and/or unburnable, possibly toxic liquids which are otherwise difficult to dispose of, for example halogenated carbons or oils, being blown in by means of the multi-functional lance or lances, thermally decomposed and thereby disposed of in an environmentally friendly manner.
By liquids are also meant, in this respect, solutions of disposable solids in corresponding solvents.
Preferably, the liquid blow-in step takes place onto the hottest point in the metallurgical vessel, and, consequently, it is particularly preferred to carry out the liquid blow-in step during a refining step or to direct the liquid jet onto the point of impingement of an arc on the melt.
In conjunction with an appropriate aftertreatment of the waste gas from the metallurgical vessel, such as, for example, quenching, the blowing-in of activated charcoal, etc., it is possible for liquids which are difficult to dispose of to be disposed of not only in an environmentally compatible way, but also profitably.
According to a further embodiment of the method according to the invention, during a refining step (C) the blown-in jet of the oxygen-containing gas is influenced in a controlled manner by the blowing-in, taking place by means of the multi-functional lance, of a further gas jet.
The subject of the invention is also a multi-functional lance for use in the method according to the invention, having a plurality of tubes which surround one another and are concentric to a central longitudinal axis and a common end of which forms the head of the multi-functional lance.
The solution for achieving the object set according to the invention depends, inter alia, on whether the multi-functional lance is to be suitable for blowing in large or small solid quantities.
For blowing in small solid quantities, the object set according to the invention is achieved by means of the combination of the following features:
a first tube (1) for forming a supply duct, in particular for solid, fine-grained to dust-like substances,
a second tube (3) surrounding the first tube (1) so as to form a first annular gap (4), in particular for the supply of an oxygen-containing gas, the mouth part (6) of the second tube (3) being designed as a Laval nozzle,
a third tube (7) surrounding the second tube (3) so as to form a second annular gap (8), in particular for the supply of gaseous and/or liquid fuel,
a fourth tube (9) surrounding the third tube (7) so as to form a third annular gap (10), in particular for the supply of an oxygen-containing gas,
a fifth tube (11) surrounding the fourth tube (9) so as to form a fourth annular gap (12), in particular for the supply of an oxygen-containing gas, the fourth annular gap (12) terminating, on the mouth side, so as to form a plurality of outflow ducts (13), and the direction of flow being directed through each outflow duct (13) away from the central longitudinal axis (2).
Particularly advantageous, here, is the first tube, through which predominantly fine-grained and/or dust-like solids are blown into and/or onto the melt or slag. Depending on the method step, in a carbon blow-in step, a supply of carbon-containing materials, in particular coal, but, for example, also coke and/or shredderlight fraction, is carried out, and, in a solid blow-in step, a supply of aggregates and/or alloying agents is carried out, by aggregates and alloying agents being meant all conventional slag formers, slag-foaming agents, agents for the oxidation of undesirable accompanying elements, agent for setting the desired composition of the metal melt, etc., which are normally used in the production of metal melts, in particular of steel and pig-iron melts. The first tube makes it possible for the multi-functional lance according to the invention to perform the carbon and solid blow-in functions.
Solids of an order of magnitude of up to 10 kg/min can be blown in by means of the multi-functional lance characterized by the above feature combination.
Since the mouth part of the second tube is designed as a Laval nozzle, the admission pressure of the oxygen-containing gas supplied during cutting and melting steps and during refining steps can be converted into a pulse, that is to say velocity. The first annular gap formed by the first and second tubes makes it possible for the multi-functional lance according to the invention to perform the cutting, melting and refining functions.
By oxygen-containing gas is preferably meant industrial oxygen, such as is obtained, for example, from an air separation plant, or air or air enriched with oxygen.
The second and third annular gaps serve, in a combustion step, for the supply of gaseous and/or liquid fuel, for example natural gas and/or fuel oil, or for the supply of oxygen-containing gas, in particular industrial oxygen, by means of which the fuel is burnt. The second and third annular gaps together make it possible for the multi-functional lance according to the invention to perform the burner function for a combustion step.
The fourth annular gap formed by the fourth and fifth tubes serves, in a post-combustion step, for the supply of oxygen-containing gas and thus makes it possible for the multi-functional lance according to the invention to perform the post-combustion function.
According to a preferred embodiment, the fourth annular gap terminates, on the mouth side, so as to form 2 to 16, preferably 4 to 6 outflow ducts.
The outflow ducts are directed away from the central longitudinal axis preferably in such a way that the normal projection of the centre axis of each outflow duct onto a plane drawn through the central longitudinal axis and through the mouth of the outflow duct forms with the central longitudinal axis an angle xcex1 of 2.5 to 25xc2x0, preferably an angle xcex1 of 5 to 15xc2x0.
By virtue of this design of the outflow ducts, by means of the oxygen-containing gas, which is fed to the atmosphere of the metallurgical vessel through the outflow ducts, a wide region of this atmosphere can be covered and burnable waste gases can be afterburnt.
According to an advantageous feature, the centre axes of the outflow ducts are skew to the central longitudinal axis of the multi-functional lance, specifically in such a way that the normal projection of the centre axis of each outflow duct onto a plane directed normally to the central longitudinal axis forms, with a plane drawn through the central longitudinal axis and through the mouth of the outflow duct, an angle xcex2 of 2.5 to 60xc2x0, preferably an angle xcex2 of 5 to 200.
This design of the outflow ducts allows an even more comprehensive post-combustion of waste gases from the metallurgical vessel, since, as a result, the oxygen-containing gas blown in via the outflow ducts and, consequently, also the waste gases from the metallurgical vessel, which are sucked into these oxygen gas jets, are set in helical rotational movement. This assists the intermixing of the oxygen-containing gas with the waste gases and the post-combustion of these.
The individual angles xcex1 and xcex2 may also be selected differently in each case for individual outflow ducts, in order to take optimally into account special boundary conditions when the multi-functional lance is used.
The outermost, that is to say fifth tube is advantageously provided with cooling which is preferably designed as a water-cooled double casing.
By means of the cooling provided according to this feature, the lifetime of the multi-functional lance is prolonged.
According to a further advantageous feature, the mouth parts of the second and/or of the third tube have slots on the outside, these slots preferably being arranged parallel to the central longitudinal axis. These slots serve for the improved cooling of the respective mouth part.
According to an advantageous design variant, the mouth parts of the first, of the second and of the third tube terminate in a first mouth plane normal to the central longitudinal axis and the mouth parts of the fourth and fifth tubes terminate in a second mouth plane normal to the central longitudinal axis, the first mouth plane being set back behind the second.
In this case, the water-cooled double casing is also expediently drawn forwards as far as the second mouth plane.
The tubes arranged inside the multi-functional lance are thereby better protected against mechanical stress at their mouth.
So that repair work can be carried out quickly and simply, the mouth end of the second tube is formed by a mouth part releasably connected, in particular screwably connected, to the second tube.
According to advantageous embodiments, the first and, if appropriate, the second tube are designed to be wear-resistant.
The wear-resistant design of the first and, if appropriate, the second tube is preferably such that the first and, if appropriate, the second tube are manufactured from an alloyed steel with chromium carbides or from a hard-chrome-plated steel or from hard-chrome-plated copper or from copper or a steel which is provided with a ceramic insert or covering on the inside and, if appropriate, on the outside.
These wear-resistant designs make it possible to blow abrasive media, such as, for example, fine-grained coal, metal oxides, slag formers and the like, through the first tube and, if appropriate, through the annular gap formed by the first and second tubes into or onto the melt or slag by means of a carrier gas, without thereby appreciably shortening the lifetimes of the first and second tubes.
So that, furthermore, repairs can be carried out particularly quickly and simply, advantageously the third and fourth tubes are divided in their length and the respective tube parts are fastened to one another by means of releasable connections, in particular screw connections.
According to a further advantageous embodiment, in addition to the mouth of the second tube, the mouth or mouths of the first and/or the third and/or the fourth tube and/or the outflow ducts are also designed as Laval nozzles.
This is expedient, in particular, in order, in addition to the refining and cutting function, also to obtain a high velocity and, consequently, pulse and range or depth of penetration of the respective gas and/or gas/solid jets for one or more of the functions, namely burner, carbon and solid blow-in and post-combustion.
The Laval nozzle form of the mouth of the second tube is expediently designed in such a way that the aperture angle xcex3 of the conical part of the mouth of the second tube is 0.1 to 5xc2x0, preferably 0.5 to 3xc2x0.
The choice of the aperture angle xcex3 also depends, inter alia, on the conditions prevailing in the melting vessel. Thus, if the melting vessel is under overpressure, somewhat lower values are selected for xcex3, whereas, in the case of a melting vessel in which underpressure or a vacuum prevails, higher values are advantageous.
As a result of a further advantageous embodiment, the first tube can be moved within the second tube along the central longitudinal axis, so that further influence can be exerted on the solid and carbon blow-in function. Furthermore, when the first tube is moved behind the contraction of the second tube, an increase in the oxygen quantity to be blown, in the case of a given admission pressure, can consequently be achieved.
In order to supply the multi-functional lance with carrier gas, the first tube as well as the first, the second, the third and the fourth annular gap are in each case connected to a carrier-gas supply, in particular an inert-gas supply.
Depending on the method step currently being carried out, carrier gas or inert gas can serve as injector gas for carbon or solid injection or for setting a specific oxygen content of the oxygen-containing gas supplied during a cutting and melting, refining or combustion step. Furthermore, the multi-functional lance, before being used in the method according to the invention, or the blowing cross sections not used at that particular time, can be scavenged with a small stream of inert gas and kept free of splashes of metal.
In order to supply the multi-functional lance with all the other gases necessary for the method steps, the first tube as well as the first, the third and the fourth annular gap are in each case connected to an oxygen supply, an air supply, if appropriate a steam supply and connectable and disconnectable solid injection and the second annular gap is connected to a fuel supply for the supply of liquid and/or gaseous fuel.
So that, if appropriate, oxygen can also be blown through the first tube, which otherwise serves predominantly for blowing coal and solids, in a cutting and melting and/or refining step, a change-over from the carrier-gas and solid supply of the first tube to the supply of oxygen can be made by means of a change-over device, in particular a change-over valve.
Advantageously, the supply of gases to the multi-functional lance can be regulated by setting the admission pressure of the respective gas.
Alternatively or additionally to this, the supply of gases to the multi-functional lance can be set by means of simple rigid diaphragms and/or quick-acting stop valves which in each case are arranged in the individual gas lines.
The object set according to the invention is achieved, furthermore, for the blowing-in of large solid quantities, by means of the combination of the following features:
a first tube for forming a supply duct, in particular for liquids or oxygen-containing gas,
a second tube surrounding the first tube so as to form a first annular gap, in particular for the supply of an oxygen-containing gas, the mouth part of the second tube being designed as a Laval nozzle,
a third tube surrounding the second tube so as to form a second annular gap, in particular for the supply of gaseous and/or liquid fuel,
a fourth tube surrounding the third tube so as to form a third annular gap, in particular for the supply of an oxygen-containing gas,
a fifth tube surrounding the fourth tube so as to form a fourth annular gap, in particular for the supply of cooling water, the fourth annular gap being designed to be closed on the mouth side,
a sixth tube surrounding the fifth tube so as to form a fifth annular gap, in particular for the supply of oxygen-containing gas, the fifth annular gap terminating, on the mouth side, so as to form a plurality of outflow ducts, and the direction of flow being directed through each outflow duct away from the central longitudinal axis,
a seventh tube surrounding the sixth tube so as to form a sixth annular gap, in particular for drawing off cooling water, the sixth annular gap being designed to be closed on the mouth side, and the fourth annular gap being connected to the sixth annular gap, in the region of the head of the multi-functional lance, by means of bores which do not cross the outflow ducts,
one to nine nozzle tubes of wear-resistant design, in particular for the supply of solid, fine-grained to dust-like substances, the nozzle tubes being arranged within the fifth annular gap and the centre axis of each nozzle tube being arranged parallel to the longitudinal axis, and the nozzle tubes piercing the head of the multi-functional lance, without crossing bores or outflow ducts.
Particularly advantageous, here, are the nozzle tubes, through which fine-grained and/or dust-like solids are blown into and/or onto the melt or slag. Depending on the method step, in a carbon blow-in step, a supply of carbon-containing materials, in particular coal, but, for example, also coke and/or shredderlight fraction, is carried out, and, in a solid blow-in step, a supply of aggregates and/or alloying agents is carried out, by aggregates and alloying agents being meant all conventional slag formers, slag-foaming agent, agent for the oxidization of undesirable accompanying elements, agent for setting the desired composition of the metal melt, etc., which are normally used in the production of metal melts, in particular of steel and pig-iron melts. The nozzle tubes make it possible for the multi-functional lance according to the invention to perform the carbon and solid blow-in functions.
The multi-functional lance characterized by the above feature combination is pre-eminently suitable for also blowing in very large solid quantities of up to 200 kg/min. This is particularly advantageous when relatively large fractions of electrical energy, which were hitherto necessary for producing the melt, are to be replaced by fossil energy, in order, for example, to increase productivity further or when relatively large quantities of the abovementioned solids are to be blown pneumatically into the slag and/or melt for a wide variety of instances of use.
Since the mouth part of the second tube is designed as a Laval nozzle, the admission pressure of the oxygen-containing gas supplied during cutting and melting steps and during refining steps can be converted into a pulse, that is to say velocity. The first annular gap formed by the first and second tubes makes it possible for the multi-functional lance according to the invention to perform the cutting, melting and refining functions.
By oxygen-containing gas is preferably meant industrial oxygen, such as is obtained, for example from an air separation plant, or air or air enriched with oxygen.
The first tube serves for the reproducible control of the pulse of the Laval jet out of the first annular gap, in that the jet propagation and, consequently, also the refining effect of the Laval jet are regulated by means of the first tube. This is also employed in order not to subject the refractory bottom of the metallurgical vessel to additional wear in the case of a low bath height or in order to ensure, in a controlled manner, higher FeO contents in slags above steel melts, so as thereby to improve appreciably the dephosphorization of the metal melts, even when the carbon contents of the melt are relatively high. The multi-functional lance according to the invention therefore also has the capability of controlling the iron oxide contents of the slags and, consequently, the dephosphorization, but, for example, also the devanadization, of the iron melt.
Liquids to be disposed of can also be injected through the first tube into the Laval jet or the focal spot in front of the multi-functional lance. The first tube thus makes it possible, inter alia, for the multi-functional lance according to the invention to perform the liquid blow-in function.
Normally, however, the first tube is loaded with oxygen or oxygen-containing gas. During the refining of alloyed melts, the first tube can be loaded with air or inert gas or steam, in order to lower the CO partial pressure at the focal spot in front of the multi-functional lance and, consequently, reduce chromium slagging.
In a combustion step, the second and third annular gaps serve for the supply of gaseous and/or liquid fuel, for example natural gas and/or fuel oil, or for the supply of oxygen-containing gas, in particular industrial oxygen, by means of which the fuel is burnt. The second and third annular gaps together make it possible for the multi-functional lance according to the invention to perform the burner function for a combustion step.
The fifth annular gap formed by the fifth and sixth tubes serves, in a post-combustion step, for the supply of oxygen-containing gas and thus makes it possible for the multi-functional lance according to the invention to perform the post-combustion function.
The lifetime of the multi-functional lance is prolonged by means of the cooling casing formed by the fourth and sixth annular gaps and by the bores connecting these annular gaps and located in the head of the multi-functional lance.
According to a preferred embodiment, the fifth annular gap terminates, on the mouth side, so as to form 2 to 16, preferably 4 outflow ducts.
The outflow ducts are directed away from the central longitudinal axis preferably in such a way that the normal projection of the centre axis of each outflow duct onto a plane drawn through the central longitudinal axis and through the mouth of the outflow duct forms with the central longitudinal axis an angle xcex1 of 2.5 to 25xc2x0, preferably an angle xcex1 of 5 to 15xc2x0.
By virtue of this design of the outflow ducts, by means of the oxygen-containing gas, which is fed to the atmosphere of the metallurgical vessel through the outflow ducts, a wide region of this atmosphere can be covered and burnable waste gases can be afterburnt.
According to an advantageous feature, the centre axes of the outflow ducts are skew to the central longitudinal axis of the multi-functional lance, specifically in such a way that the normal projection of the centre axis of each outflow duct onto a plane directed normally to the central longitudinal axis forms, with a plane drawn through the central longitudinal axis and through the mouth of the outflow duct, an angle xcex2 of 2.5 to 60xc2x0, preferably an angle xcex2 of 5 to 20xc2x0.
This design of the outflow ducts allows an even more comprehensive post-combustion of waste gases from the metallurgical vessel, since, as a result, the oxygen-containing gas blown in via the outflow ducts and, consequently, also the waste gases from the metallurgical vessel, which are sucked into these oxygen gas jets, are set in a helical rotational movement. This assists the intermixing of the oxygen-containing gas with the waste gases and the post-combustion of these.
The individual angles xcex1 and xcex2 may also be selected differently in each case for individual outflow ducts, in order to take optimally into account special boundary conditions when the multi-functional lance is used.
The Laval nozzle form of the mouth of the second tube is expediently designed in such a way that the aperture angle xcex3 of the conical part of the mouth of the second tube is 0.1 to 5xc2x0, preferably 0.5 to 3xc2x0.
The choice of the aperture angle y also depends, inter alia, on the conditions prevailing in the melting vessel. Thus, if the melting vessel is under overpressure, somewhat lower values are selected for xcex3, whereas, in the case of a melting vessel in which underpressure or a vacuum prevails, higher values are advantageous.
According to a further advantageous feature, the mouth parts of the second and/or of the third tube have slots on the outside, these slots preferably being arranged parallel to the central longitudinal axis. These slots serve for the improved cooling of the respective mouth part.
According to an advantageous design variant, the mouth parts of the second and of the third tube terminate in a first mouth plane normal to the central longitudinal axis and the mouth parts of the fourth, fifth, sixth and seventh tube terminate in a second mouth plane normal to the central longitudinal axis, the first mouth plane being set back behind the second.
The tubes arranged inside the multi-functional lance are thereby better protected against mechanical stress at their mouth.
As a result of a further advantageous embodiment, the first tube can be moved within the second tube along the central longitudinal axis, so that further influence can be exerted on the Laval jet from the first annular gap. Furthermore, when the first tube is moved behind the contraction of the second tube, an increase in the oxygen quantity to be blown, in the case of a given admission pressure, can consequently be achieved.
So that repairs can be carried out quickly and simply, the mouth end of the second tube is formed by a mouth part releasably connected to the second tube, in particular connected to it screwably or by means of a sliding connection sealed off by means of O-rings.
So that, furthermore, repairs can be carried out particularly quickly and simply, advantageously the third and/or the fourth and/or the fifth and/or the sixth and/or the seventh tube are divided at least once in their length and the respective tube parts are fastened to one another by means of releasable connections, in particular screw connections and/or sliding connections sealed off by means of O-rings.
According to a further advantageous embodiment, in addition to the mouth of the second tube, the mouth or mouths of the third and/or of the fourth tube and/or the outflow ducts and/or the mouth or mouths of the nozzle tube or nozzle tubes are also designed as Laval nozzles and/or the mouth of the first tube is widened in diameter.
This Laval nozzle form is expedient, in particular, in order, in addition to the refining and cutting function, also to obtain a high velocity and, consequently, pulse and range or depth of penetration of the respective gas and/or gas/solid jets for one or more of the functions, namely burner, carbon and solid blow-in and post-combustion.
The widening of the mouth diameter of the first tube is advantageous, in particular, in the case of a melting vessel which is under underpressure or a vacuum.
According to an advantageous embodiment, the nozzle tube or nozzle tubes is or are designed to be wear-resistant.
The wear-resistant design of the nozzle tubes is preferably such that the respective tube is manufactured from an alloyed steel with chromium carbides or from a hard-chrome-plated steel or from hard-chrome-plated copper or from copper or a steel which is provided with a ceramic insert or covering on the inside and, if appropriate, on the outside.
These wear-resistant designs make it possible to blow abrasive media, such as, for example, fine-grained coal, metal oxides, slag formers and the like, through the nozzle tubes into or onto the melt or slag by means of a carrier gas, without thereby appreciably shortening the lifetimes of the nozzle tubes.
In a further advantageous embodiment of the multi-functional lance according to the invention, a solid-distribution chamber is assigned to the nozzle tube or nozzle tubes at that end which faces away from the head of the multi-functional lance, the solid-distribution chamber being formed by an annular, essentially cylindrical hollow body enclosed all-round and having a bottom, a cover and a lateral limitation, and the nozzle tube or nozzle tubes piercing the bottom of the solid-distribution chamber from below, and at least one solid supply opening tangentially into the lateral limitation of the solid-distribution chamber.
In addition to the above embodiment, a further annular, essentially cylindrical hollow body is preferably provided, the further hollow body being open at the top and having a bottom and a lateral limitation, and the further hollow body being arranged within the solid-distribution chamber in such a way that a gap remains between the cover of the solid-distribution chamber and the lateral limitation of the further hollow body, and the nozzle tube or nozzle tubes opening into the bottom of the further hollow body.
Solid is blown tangentially into the solid-distribution chamber and f lows through the gap via an intermediate wall, formed by the lateral limitation of the further hollow body, into a space, from which the nozzle tubes lead away (that is to say, into the further hollow body). The entry to the nozzle tubes is conical and, like the nozzle tubes themselves, is designed to be wear-resistant.
The solid-distribution chamber is fastened to the lance body by means of a quick-acting fastening or a flange and, after the fastening has been released, can be drawn off. The wear-resistant nozzle tubes are fastened in a ring forming the bottom of the solid-distribution chamber and can easily be exchanged.
The solid-distribution chamber of the multi-functional lance according to the invention is expediently connected to a carrier-gas supply, in particular an inert-gas supply, and to one or more solid supplies.
Alternatively to this, that is to say when no solid-distribution chamber is provided, the nozzle tubes themselves are connected to a carrier-gas supply, in particular an inert-gas supply, and to one or more solid supplies.
For the further supply of the multi-functional lance with carrier gas, the first tube as well as the first, the second, the third and the fifth annular gap are in each case connected to a carrier-gas supply, in particular an inert-gas supply.
Depending on the method step currently being carried out, carrier gas or inert gas may serve as injector gas for carbon or solid injection or for setting a specific oxygen content of the oxygen-containing gas supplied during a cutting and melting, refining or combustion step. Furthermore, the multi-functional lance, before being used in the method according to the invention, or the blowing cross sections not used at that particular time, can be scavenged with a small stream of inert gas or with air and be kept free of splashes of metal.
In order to supply the multi-functional lance with all the other gases necessary for the method steps, the first tube as well as the first, the third and the fifth annular gap are in each case connected to an oxygen supply, an air supply and, if appropriate, a steam supply, and the second annular gap is connected to a fuel supply for the supply of liquid and/or gaseous fuel.
Additionally or alternatively to the supply of oxygen and/or air, the first and/or the fifth annular gap may be provided with a hot-blast supply. By hot blast is to be meant, in this case, an oxygen-containing gas, for example air enriched with oxygen, at a temperature of 200 to about 1200xc2x0 C.
Advantageously, the supply of gases to the multi-functional lance can be regulated by setting the admission pressure of the respective gas.
Alternatively or additionally to this, the supply of gases to the multi-functional lance can be set by means of simple rigid diaphragms and/or quick-acting stop valves which in each case are arranged in the individual gas lines.
All the embodiments of the multi-functional lances according to the invention have in common the fact that, as is known per se, electromagnetic waves, in particular in the range of visible light and of the adjacent infrared range, which are emitted by a metal melt, can, through the first tube and/or the first annular gap, be capable of being detected by means of an optical system and of being fed to a detector for determining the temperature and/or chemical composition of the metal melt.
During such measurements, preferably inert gas is blown through the first tube and/or the first annular gap, and, at the same time, the burner function of the multi-functional lance can remain switched on. In this case, the evaluation of the electromagnetic waves for determining the temperature and/or chemical composition of the metal melt may be carried out by pyrometry and/or spectrometry. A similar method has already been proposed in WO 97/22859, the difference being that, here, measurement is not carried out under the bath, as in WO 97/22859.
The multi-functional lances according to the invention, in both the embodiment for smaller solid quantities and that for larger solid quantities, are advantageously arranged in such a way that they are displaceable and/or pivotable along their longitudinal axis. Consequently, on the one hand, the depth of penetration of the respective gas jets into the melt can be controlled and the running distance of the gas jets, in the case of a variable height of the bath surface, can be set, and, on the other hand, a larger region of the bath surface can be reached or swept.
It has proved advantageous, furthermore, to arrange a multi-functional lance below a copper panel bulged in the direction of the interior of the metallurgical vessel, the multi-functional lance remaining displaceable and/or pivotable, since it is thereby protected particularly well.
The number of multi-functional lances used in a metallurgical vessel for the method according to the invention varies with the type of metallurgical vessel and its size and with the embodiments of the multi-functional lances used. One to 10 multi-functional lances may be provided. The investment costs, which are higher in the case of larger numbers, are more than compensated by the fact that the introduction of energy, of carbon and of solids and the post-combustion take place in an essentially equalized manner over the entire furnace space or the entire melt surface and the productivity of the respective metallurgical vessel is increased.
In the case of relatively large numbers of multi-functional lances, for example 5, it is also advantageous for the multi-functional lances to be designed with smaller dimensions, so that the sum of the blowing cross sections is approximately the same as when a smaller number of multi-functional lances, for example only two multi-functional lances, are used.
The electric furnace and the converter are adopted hereafter as typical, but non-restrictive examples for describing the invention.
Unless specified otherwise, the following statements relate to multi-functional lances for blowing in relatively large solid quantities.
In order to simplify the terminology, the first tube, the first, the second, the third and fifth annular gaps and the nozzle tubes, together with the respectively associated mouth part and the outflow ducts, are designated hereafter as nozzle1, nozzle2, nozzle3, nozzle4, nozzle5 and nozzle6.
According to the invention, one or, in the case of larger furnaces, a plurality of multi-functional lances are arranged above the bath surface, as measured before the tapping of the melt, preferably in the side wall, in the bay region or else so as to blast from the furnace roof. The longitudinal axis of the multi-functional lance, if it is arranged in the side wall or in the bay region, is to have an inclination relative to the bath surface of more than 35xc2x0. The multi-functional lance is, as a rule, arranged in a stationary manner. In the case of an arrangement in electric furnaces with long bricks in the slag zone or sometimes also in the bay region of the electric furnace, a linearly displaceable lance arrangement, with or without the possibility of pivoting, is provided in the side wall and/or in the bay region or in the furnace roof.
Depending on how the electric furnace is equipped with burners and/or post-combustion lances corresponding to the prior art, the multi-functional lances are used preferably in the area of the colder furnace regions (cold spots) or bay. In principle, however, the multi-functional lances may be used at all points on the furnace circumference or so as to travel down from the furnace roof. In the case of electric furnaces which are charged, for example continuously, with large quantities of sponge iron through a fifth roof hole, it is advantageous to have an arrangement in which the jets from the multi-functional lances impinge in the vicinity of the point of impingement of the sponge iron on the melt, since energy is urgently required there, CO occurs and can be afterburnt and the formation of FeO is reduced by blowing in coal.
As regards the height of the lance position in the side wall, it must be stipulated that the running distance of, for example, the jet from nozzle2 is to be less than 2 m, if the specific refining of the melt and, consequently, the penetration of the oxygen jet into the melt are important. In the bay of the electric furnace, the running distance of the jets is mostly below 1.2 m. In the converter or similar reactors, the running distances of the jets may even be substantially longer than 2 m.
In order to optimize the electrode consumption, the multi-functional lances, when arranged in the side wall, are preferably arranged tangentially to an imaginary cylinder. The cylinder diameter is between the electrode reference circle and the furnace wall.
The multi-functional lance is preferably inserted into an intensively cooled, approximately square copper panel having a side length of about 0.5 m. The lifetime of the surroundings of the lance is thereby lengthened. This is important, in particular, when sometimes large scrap fragments are in use and the preheating time during blasting with oxygen from nozzle4 and fuel from nozzle3 is kept short. Then, in particular, the oxygen jet from nozzle5 or else nozzle2 can be deflected and for a short time a part quantity can brush the panel, as may also occur in conventional burners. Installing the multi-functional lance below a copper panel bulged in a wedge-shaped manner in the direction of the furnace interior has proved particularly advantageous, since the lance is thereby protected particularly well.
Operation with the multi-functional lance according to the invention may be described as follows:
In the stand-by position, the nozzles are loaded with the media, air (nozzle1), air (nozzle2), N2 (nozzle3), air (nozzle4) and air (nozzle5) in minimal quantities which, for example, flow at 0.2 bar.
During charging, the pressure at the nozzles is increased briefly to about 1.5 bar when the lance is exposed to splashes from the furnace space during charging.
After the charging of iron carriers, such as scrap and/or cast iron, and of lump coal, directly reduced iron, slag formers, etc., the multi-functional lance is activated in steps, starting from the keeping-clear quantities (an admission pressure of below 1 bar) and is used for the various purposes. However, the time flow of the method steps also depends, inter alia, on the lumpiness of the feed substances, the planned profile of the carbon content of the melt, the metal oxide contents in the slag, the necessary dephosphorization of the melt, etc. and may vary. In the extreme instance, all the functions are switched on from the outset and the lance is operated constantly for a period of time.
In the case of average feed substancesxe2x80x94conventional scrapxe2x80x94, typical operation is as follows:
First, after the ignition of the arc and flaming in the waste-gas elbow, oxygen through nozzle4 is switched on and, immediately thereafter, the fuel, such as, for example, natural gas (0.6 to 7 Nm3/min), from nozzle 3 is connected. The scrap is preheated upstream of the lance (burner function).
After a short time, which depends on the scrap mix used, for example after two minutes, a mean oxygen throughflow from nozzle2 for the cutting and oxidizing melting of the scrap is switched on. Depending on the precalculated O2 quantity for refining, after a metal sump having a depth of, for example, 20 cm has been formed, the melt is decarbonized with a larger quantity of oxygen by means of an oxygen-jet pulse controlled by the first tube. In this case, the burner function remains switched on in most instances of use, in order to optimize the effectiveness of melting and decarbonization and of the partial oxidization of the melt.
After the oxygen from nozzle5 has been connected, the burnable furnace gases are sucked into the individual oxygen jets and partially burnt. The energy released at the same time is transmitted with high efficiency to the scrap, slag and melt and is not lost to the waste-gas system. The latter is even relieved of thermal load. The oxygen jets from nozzle5, that is to say 2 to 16 jets per multi-functional lance, blow askew away from the longitudinal axis of the lance downwards into the scrap running gear.
In a lance for low solid blow-in rates, the central nozzle1 can, if a special change-over valve is installed at the entrance to the nozzle, be changed over from air to the oxygen mode and, after being scavenged with nitrogen, to, for example, the blowing-in of coal. When there is a high demand for oxygen for refining purposes, coal injection is switched off, nozzle1 is scavenged with N2 with the aid of the change-over valve, and nozzle1 and nozzle2 are loaded with a predetermined oxygen throughflow.
The oxygen quantity through nozzle2 is 400 to 3000 Nm3 per hour, depending on the furnace size and the number of multi-functional lances. Up to 0.3 kg/min of coal are blown through the nozzles6 per mm2 of blowing cross section. Depending on the operating mode, therefore, the melt can either be quickly refined or even carbonized. Through a nozzle6 with a nominal width of 12 mm, it is possible, for example, to blow up to 34 kg/min of coal when low O2 quantities are blown through nozzle2. By coal blasting, the slag is foamed very quickly and intensively, the FeO contents in the slags are stabilized at a low level to below 20%, and, even in the case of carbon contents of the melt of, for example, 0.04%, the oxygen contents in the steel are reduced from about 1000 to about 600 ppm. This also leads, inter alia, to lower consumptions of alloying agents and to a purer steel. These effects may be reinforced by scavenging the melt with accurately regulatable scavenging nozzles which are loaded with nitrogen and/or argon plus CH4.
When low carbon contents of the melt of, for example, 0.03% have to be set and the slag must also foam in the superheating period of the melt, the coal is blown onto the slag through nozzle6 only at very low pressure and with a small quantity/min and is thereafter refined again.
When relatively large carbon quantities are to be briefly supplied to the melt or, for conditioning, to the slag, inert gas, air or small oxygen quantities are blown through nozzle2 and large coal quantities through nozzle6. The pressure at the entrance to nozzle6 rises with the blowing-in of coal (or else the blowing-in of solid) according to the following rule of thumb:       f    =                            1.4          +          B                1.4              ;
in this, f represents the factor for the pressure rise in the case of a constant carrier-gas quantity and B represents the carrier-gas content in kg/Nm3.
Particularly in the case of Cr-alloyed melts, the reduction in the CO partial pressure and, consequently, in Cr slagging in the case of carbon contents of, for example, below 1% due to the admixture of inert gas or steam to the oxygen from nozzle1, nozzle2 and nozzle4 is particularly advantageous.
As a result, carbon contents to below 0.4% can be produced efficiently, that is to say with a low degree of slagging of the alloying elements, at low temperature and with high productivity. Subsequent VOD treatment (Vacuum Oxygen Degassing) is thereby shortened appreciably and the entire productivity of the method route EAF, with a multi-functional lance or multi-functional lances and VOD, is increased substantially. Bottom blowing by means of oxygen and inert gas or steam, in combination with the multi-functional lances, is a particularly suitable combination for making alloyed steel, such as, for example, stainless steel, in the EAF, using the present method. In an extreme instance, stainless steel can be made in such an EAF, even without VOD treatment.
The multi-functional lances according to the invention and their use are explained in more detail hereafter in FIG. 1 to FIG. 9 of the drawings.
In this case, FIG. 1 to FIG. 3 of the drawings illustrate the multi-functional lance for blowing in relatively small solid quantities: